The object of this project is to study the etiology and pathogenesis of mucosal diseases of the oral cavity, with the ultimate goal of treatment and prevention. At the present time, emphasis is on recurrent aphthous ulcers, Behcet's disease, and Sjogren's syndrome. Efforts are being made, by a variety of techniques, to demonstrate a viral etiology and to look for immunological abnormalities. Attempts also are being made to transmit the disease to rhesus monkeys. Experiments were begun to determine if injury to tissue plays a role in initiating oral ulcers in patients known to have recurrent disease, as compared to matched controls. Double-blind clinical trials are being carried out to determine the efficacy of various drugs.